1. Field of the Invention
The present invention relates to a cam switch of the type comprising an operating member provided with a rotary coupling shank; a trip unit housing a trip mechanism operatively connected to the coupling shank; a number of pack-aligned switching units contiguously fixed to the trip unit and each provided with contact means comprising fixed and movable contacts, the latter being movable, in opposition to the action exerted by counter springs, from a closure position in which the movable contacts come in contact with the fixed contacts and a break condition in which the movable contacts are spaced apart from the fixed contacts; a drive shaft operatively connected to said trip mechanism and provided with a rotating motion by the coupling shank in order to cause the translation of the movable contacts through cams associated therewith and a terminal closure element fixed to the switching unit opposite the trip unit and rotatably supporting the drive shaft at one free end thereof.
2. Prior Art
It is known that cam switches substantially comprise a number of consecutively pack-aligned switching units provided each with two or more pairs of fixed contacts leading off to respective electric circuits, and movable contacts designed to act on the fixed contacts to selectively close and break the above mentioned electric circuits.
The operation of the fixed contacts is performed by a drive shaft rotatably engaged through the switching units and provided with a plurality of cams. Each of said cams is associated with a switching unit in order to produce, due to the rotation motions imparted to the drive shaft, the translation of the movable contacts from a closure condition in which the movable contacts are in contact with the fixed contacts to a break condition in which the movable contacts are suitably spaced apart from the fixed contacts. The above mentioned translation takes place in opposition to the action carried out by countersprings acting on the movable contacts. One end of the drive shaft is rotatably supported by a terminal closure element fastened to the switching units and its opposite end is operatively engaged with a trip mechanism being part of a trip unit secured to the switching units on the opposite end of the terminal element. The trip unit substantially acts such as to give the drive shaft predetermined angular positionings when the latter is rotated by means of suitable manually or electrically actuated operating members.
Currently the switching units, trip unit and terminal closure element are mutually engaged, in pack-alignment, by means of two or more threaded tie rods extending through the same over the whole length of the pack. The length of said tie rods must therefore be calculated depending upon the whole pack length which can undergo very wide variations depending on the number of the switching units forming the switch. This factor involves many problems resulting from the fact that it is necessary to accomplish many types of tie rods having different lengths each of them being fit for the assembly of a specific switch.
Traditional switches also have several further drawbacks due to the fact that the drive shaft arranged therein is of one piece construction. Therefore, as in the case of the tie rods, the length of the drive shaft must be calculated depending on the whole switch length.
In addition in many cases the length of the drive shaft must also be calculated depending on the thickness of the support panel to which the switch has to be fastened. This is for example the case of a drive shaft extending beyond the switch so that it may rotatably cross the support panel and engages a knob or the like allowing the switch to be operated.
Therefore at the present state of the art it is also necessary to manufacture many drive shafts having different lengths in order to meet the different requirements concerning operation and installation.
The presence of the above described tie rods and drive shaft also involves some problems when a switch has to be modified, for example by the addition or removal of one or more switching units. In this case, together with the addition or removal of the switching units, it is also necessary to carry out the replacement of the drive shaft and tie rods.
Moreover and above all, still referring to the above mentioned necessary modifications, it is to be noted that, as a result of the structure of current switches, the removal of the tie rods brings about the whole diassembly of the switch, as regards both the mutual connection between trip unit, switching units and terminal element and the connection between the single elements forming the trip and switching units. In this connection it must be in fact pointed out that a stable positioning of these elements is achieved only when the switch is thoroughly assembled and it is therefore subjected to be impaired when either the switching units or trip unit to which said elements belong are severed from the adjoining units.
For the above reasons it has not proved to be convenient till now to alter an existing switch by adding switching units thereto or removing them therefrom and/or by replacing the trip unit and the closure element.